Volcano Review

Volcanoes and Plate Tectonics

What is a volcano? A mountain that forms when
magma reaches the surface of the Earth.

Magma - molten rock, gas, and water in the mantle

Lava- magma when it reaches the surface (cools to
form solid rock)

Where are Volcanoes Found?

Ring of Fire
Major belt of volcanoes
that circles the Pacific
Ocean

Volcanoes are found along plate boundaries

How Volcanoes Form

Island arc:

A string of islands
at an ocean-ocean
convergent plate
boundary

Hot Spots: Magma erupts
from the mantle through
the crust and reaches the
surface

Examples:
1.

Yellowstone National Park

2.

Hawaii islands

Where are Volcanoes Found?

Volcanic Eruptions

Geologists classify
volcanoes as

Quiet or Explosive.

...It depends on silica
content and
temperature.

Volcano Eruptions & Classification

What happens when a Volcano Erupts?

Example: Kilauea volcano, Hawaiian Islands

Quiet Eruptions:
● Low silica
● Thin and runny
● Flows easily
● Gas bubbles let

out gently

Hawaii → Quiet Eruption

What happens when a Volcano Erupts?

Example:
Mount Saint Helens, Oregon

Explosive Eruptions:
● High silica
● Thick & sticky
● Magma builds up &

gets pushed out with
great force!

● Gases get trapped
● Throws lava in the air

breaks into fragments
of ash, cinders,
bombs.

Mount St. Helens → Explosive Eruption

Pahoehoe Lava
(pah HOH ee hoh ee)

Fast moving hot lava that
is thin and runny

Solid mass of ropelike coils

Volcano Erupts- Types of Lava

(From Quiet Eruption)

Aa Lava
(AH ah)

Cooler
and
thicker

Slower
moving

Rough
jagged lava
chunks

Volcano Erupts- Types of Lava

Volcanic Landforms

Cinder Cone Volcanoes:

●Magma thick & sticky

●Erupt explosively

Composite Volcanoes:

●Silica varies

●Eruptions alternate with flows
and explosive

Shield Volcanoes:

●Thin layers of lava

●Hot spot volcanoes, ocean floor

Volcanic eruptions create landforms made of lava, ash, and other materials

Cinder Cone
Volcano

● High silica

content

● Thick & sticky

magma

● Explosive

volcano

● Steep, cone

shaped hill

Volcanic Landforms:

Composite
Volcanoes
●

Varying silica
content

●

magma
thickness varies

●

Alternating
layers of lava
and ash

●

Tall, cone
shaped
mountains

Volcanic Landforms:

Shield
Volcanoes

● Thin layers of

lava

● Wide, gently

sloped
mountain

Volcanic Landforms:

NOTE: Hot Spot volcanoes that form on the ocean
floor are usually shield volcanoes.